In the fabrication of most semiconductor IC packages, a chip or die is mechanically and electrically connected to the leads of a package substrate prior to encapsulating the device in a protective package. Electrical contact is made between the conductive pads on the active face of the chip and external leads of the substrate. The two major pieces of automated equipment, i.e. chip and wire-bonders, used to connect the chip and substrate have many variations, but are similar in that the work stations of each apparatus must hold the device under assembly securely in place during such processing.
In the operation of a chip-bonder, a substrate is positioned onto a workstation where a semiconductor chip is adhered to the substrate. Failure to secure the substrate in a flat and horizontal position during chip mounting can cause the chip to be misplaced and/or tilted, which subsequently can lead to failures at the wire-bonding process. During other processing steps, an automated wire-bonder interconnects the input/output (I/O) pads of a semiconductor chip to specified leads on the substrate by fine wires. As with chip mounting, the substrate must be held securely in the proper position so that the chip and the leads to be bonded are properly oriented. Failure to properly hold the substrates and chips during wire-bonding often results in poorly formed bonds, broken or lifted wires.
As the manufacturing of IC packages has become more diverse and complex, the substrates are usually thinner, and thus the necessity to provide a flat, parallel surface has become more challenging. Specifically, in older technologies the substrates were rigid materials, such as ceramics or thick metal lead frames. However, in more current devices substrates often are made of a flexible film, a thin composite or laminate polymer, or a thin lead frame of malleable material, all of which commonly tend to conform to warped or otherwise misshaped carriers (or “boats”) used to transport the substrates during various stages of processing. Thus, the end result of such warping by the package substrates can contribute to non-uniform bond line thickness of chip adhesives, tilted chips during chip mount, and broken or poorly formed bonds, all of which are unacceptable for reliable, high yield processing. Accordingly, what is needed are techniques and equipment for detecting such warping before crucial processing steps are performed so that appropriate action can be taken to increase yield.